Chemiluminescent acridinium dimethylphenyl esters are highly sensitive labels (FIG. 1B) that are used for the measurement of a wide range of clinically important analytes in automated immunoassays such as Siemens Healthcare Diagnostics' ADVIA: Centaur® systems. At the end of each assay, light emission from the acridinium ester label is triggered by the sequential addition of two reagents. An initial treatment with 0.3 mL of 0.1 M nitric acid (also containing 0.5% hydrogen peroxide) converts the non-chemiluminescent pseudobase of the acridinium ester (FIG. 1A) to the chemiluminescent acridinium form of the label. Subsequent addition of 0.3 mL of 0.25 M sodium hydroxide also containing 7 mM of the cationic surfactant cetyltrimethylammonium chloride (CTAC), ionizes the hydrogen peroxide and initiates light emission. The surfactant CTAC plays a very important role in the chemiluminescence process of acridinium esters (Natrajan et al, Org. Biomol. Chem., 2011, 9, 5092-5103). CTAC compresses emission times of the labels from approximately 60 s to <5 seconds. CTAC also increases overall light output 3-4 fold from acridinium ester labels and their conjugates. Faster light emission and increased light output enable fast and sensitive assays in automated instruments such as in Siemens Healthcare Diagnostics' ADVIA: Centaur® systems.
Each immunoassay test performed on the ADVIA: Centaur® system consumes approximately 0.7 mg of CTAC. The very large volume of immunoassay tests that are performed worldwide on the ADVIA: Centaur® systems (>500 million tests in 2012 alone based on one estimate) results in the annual usage of substantial quantities (>350 kg) of this cationic surfactant. Cationic surfactants such as CTAC are considered to be quite toxic to aquatic life when they are discharged into the environment (Nacz-Jawecki et al, Ecotoxicology and Environmental Safety, 2003, 54, 87-91; Pantani et al, Bull. Environ. Contamin. Toxicol., 1995, 55, 179-186; Kümmurer et al, J. Chromatogr. A, 1997, 774, 281-286; Sütterlin et al, Ecotoxicology and Environmental Safety, 2008, 71, 498-505; Roberts and Costello, QSAR, 2003, 22, 220-225; Leeuwen et al, Chemosphere, 1992, 24, 629-639). Although cationic surfactants are degraded by microbes under aerobic conditions, under anaerobic conditions they are persistent and show little biodegradation thereby posing a serious environmental risk to aquatic life (Ying, Environment International, 2006, 32, 417-431; Maden in Biodegradability and Toxicity of Surfactants, Handbook of Detergents Part B: Environmental Impact, U. Zoller, Editor, Marcel Dekker, 2004, p 211-248; Ying in Distribution, Behavior, Fate and Effects of Surfactants and their Degradation Products in the Environment, Handbook of Detergents Part B: Environmental Impact, U. Zoller, Editor, Marcel Dekker, 2004, p 77-109).
Thus, a long-felt need remains to replace CTAC with degradable and environment friendly (“green”) surfactants, while preserving the efficiency of chemiluminescence enhancement. It is therefore an object of the present invention to provide green surfactants that are at least as efficient as CTAC in enhancing chemiluminescence.